VMIR is a standalone library written in C that can parse and execute LLVM bitcode (.bc) files. Optionally it can generate machine code (JIT) to speed up execution significantly. JIT is currently only supported on 32 bit ARM.
To build VMIR just type:
$ make
... and you will end up with a vmir binary in very same directory. The library is compiled from a single file src/vmir.c which in turn include other files to keep stuff somewhat separated.
Let's create a small program and run it. Type the following well known snippet into a file called helloworld.c
int main(void)
{
printf("Hello world\n");
return 0;
}
Then compile it
clang -emit-llvm -target le32-unknown-nacl -c helloworld.c -o helloworld.bc
And finally, run it:
$ ./vmir helloworld.bc
Hello world
Interpretion is about 10x slower (on x86) than the same binary compiled as native code. Still it's a lot faster than LLVM's own interpreter (which by all means is not intended to run code fast in any way)
Example run of test/misc/src/sha1test.c over 64MB of random data
| Environment | (Core i7 3.2GHz) | ARMv7 BCM2709 (Rpi2) |
|---|---|---|
| Native | 0.39s | 3.54s |
| VMIR JIT | n/a | 17.5s |
| VMIR | 4.8s | 1m 42s |
| LLVM LLI | 7m 39s | n/a |
VMIR currently passes the gcc torture test suite on optimization level 0, 1 and 2. Those tests can be found in test/gcc-torture. Use make && ./runtest to run the tests.
- It only work on little endian machines.
- The built-in libc is lacking a lot of functions and features. This is where most work needs to be done.
- No support for vector types (Ie, code must be compiled with
-fno-vectorize -fno-slp-vectorize). - Not all instructions classes / value types are JITed.
- No C++ STL solution. Ideas welcome...
VMIR uses the same target as Google NativeClient. There are small examples in test/misc.
When building bigger projects consisting of multiple files you must llvm-link to combine the .bc files into a single file.
Including VMIR in your own project is pretty straight forward. Just copy the files from src/ to your project but only compile vmir.c (it will include all other .c -files on its own). The API is defined in vmir.h. See src/main.c for example how to load and execute binaries.
VMIR's libc also offers an option to use TLSF for memory allocation. The default built-in allocator is a very simple linear search first-fit algorithm.
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